In vitro and in vivo comparative performance studies of gadolinium-loaded zeolites and Gd-DOTA as contrast agents for MRI applications

Gadolinium-based contrast agents (CAs) were synthesized using faujasite zeolite (NaX) and zeolite beta (BEA) and their performances in vitro and in vivo were compared to the widely used commercial CA, gadoteric acid (Gd-DOTA). Magnetic resonance imaging (MRI) relaxometry studies (considering longitudinal [T₁ ] and transverse [T₂ ] relaxation times) were performed using Gd-DOTA and the zeolitic materials loaded with Gd³⁺ . The Gd-loaded NaX, which presented large pores and cavities (7.35 and 11.24 Å, respectively), exhibited relaxivity values of around 52 mM^-1 s^-1 , while BEA, which presented smaller pore and cavity diameters (5.95 and 6.68 Å, respectively) showed lower relaxivity values of ~4.8 mM^-1 s^-1 . The effect of the Gd-loaded NaX as MRI CA was tested in vivo in Sprague-Dawley rats, employing a 7 T scanner, with comparison to Gd-DOTA MRI angiography. The relaxivity measurements showed that the Gd-loaded NaX (50 mM^-1 s^-1 ) provided better image contrast than Gd-DOTA (5.1 mM^-1 s^-1 ). Clearance studies of the CAs using urine and blood showed that both Gd-loaded NaX and Gd-DOTA were eliminated from the body after 2 days, demonstrating the potential of Gd-loaded NaX for use as an MRI CA.

Deep-Learning-Based Neural Tissue Segmentation of MRI in Multiple Sclerosis: Effect of Training Set Size

BACKGROUND

The dependence of deep-learning (DL)-based segmentation accuracy of brain MRI on the training size is not known.

PURPOSE

To determine the required training size for a desired accuracy in brain MRI segmentation in multiple sclerosis (MS) using DL.

STUDY TYPE

Retrospective analysis of MRI data acquired as part of a multicenter clinical trial.

STUDY POPULATION

In all, 1008 patients with clinically definite MS.

FIELD STRENGTH/SEQUENCE

MRIs were acquired at 1.5T and 3T scanners manufactured by GE, Philips, and Siemens with dual turbo spin echo, FLAIR, and T1 -weighted turbo spin echo sequences.

ASSESSMENT

Segmentation results using an automated analysis pipeline and validated by two neuroimaging experts served as the ground truth. A DL model, based on a fully convolutional neural network, was trained separately using 16 different training sizes. The segmentation accuracy as a function of the training size was determined. These data were fitted to the learning curve for estimating the required training size for desired accuracy.

STATISTICAL TESTS

The performance of the network was evaluated by calculating the Dice similarity coefficient (DSC), and lesion true-positive and false-positive rates.

RESULTS

The DSC for lesions showed much stronger dependency on the sample size than gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF). When the training size was increased from 10 to 800 the DSC values varied from 0.00 to 0.86 ± 0.016 for T2 lesions, 0.87 ± 009 to 0.94 ± 0.004 for GM, 0.86 ± 0.08 to 0.94 ± 0.005 for WM, and 0.91 ± 0.009 to 0.96 ± 0.003 for CSF.

DATA CONCLUSION

Excellent segmentation was achieved with a training size as small as 10 image volumes for GM, WM, and CSF. In contrast, a training size of at least 50 image volumes was necessary for adequate lesion segmentation.

LEVEL OF EVIDENCE

1 Technical Efficacy Stage: 1 J. Magn. Reson. Imaging 2020;51:1487-1496.

Are multi-contrast magnetic resonance images necessary for segmenting multiple sclerosis brains? A large cohort study based on deep learning

BACKGROUND

Magnetic resonance images with multiple contrasts or sequences are commonly used for segmenting brain tissues, including lesions, in multiple sclerosis (MS). However, acquisition of images with multiple contrasts increases the scan time and complexity of the analysis, possibly introducing factors that could compromise segmentation quality.

OBJECTIVE

To investigate the effect of various combinations of multi-contrast images as input on the segmented volumes of gray (GM) and white matter (WM), cerebrospinal fluid (CSF), and lesions using a deep neural network.

METHODS

U-net, a fully convolutional neural network was used to automatically segment GM, WM, CSF, and lesions in 1000 MS patients. The input to the network consisted of 15 combinations of FLAIR, T1-, T2-, and proton density-weighted images. The Dice similarity coefficient (DSC) was evaluated to assess the segmentation performance. For lesions, true positive rate (TPR) and false positive rate (FPR) were also evaluated. In addition, the effect of lesion size on lesion segmentation was investigated.

RESULTS

Highest DSC was observed for all the tissue volumes, including lesions, when the input was combination of all four image contrasts. All other input combinations that included FLAIR also provided high DSC for all tissue classes. However, the quality of lesion segmentation showed strong dependence on the input images. The DSC and TPR values for inputs with the four contrast combination and FLAIR alone were very similar, but FLAIR showed a moderately higher FPR for lesion size <100 μl. For lesions smaller than 20 μl all image combinations resulted in poor performance. The segmentation quality improved with lesion size.

CONCLUSIONS

Best performance for segmented tissue volumes was obtained with all four image contrasts as the input, and comparable performance was attainable with FLAIR only as the input, albeit with a moderate increase in FPR for small lesions. This implies that acquisition of only FLAIR images provides satisfactory tissue segmentation. Lesion segmentation was poor for very small lesions and improved rapidly with lesion size.

Deep Learning for Predicting Enhancing Lesions in Multiple Sclerosis from Noncontrast MRI

Background Enhancing lesions on MRI scans obtained after contrast material administration are commonly thought to represent disease activity in multiple sclerosis (MS); it is desirable to develop methods that can predict enhancing lesions without the use of contrast material. Purpose To evaluate whether deep learning can predict enhancing lesions on MRI scans obtained without the use of contrast material. Materials and Methods This study involved prospective analysis of existing MRI data. A convolutional neural network was used for classification of enhancing lesions on unenhanced MRI scans. This classification was performed for each slice, and the slice scores were combined by using a fully connected network to produce participant-wise predictions. The network input consisted of 1970 multiparametric MRI scans from 1008 patients recruited from 2005 to 2009. Enhanced lesions on postcontrast T1-weighted images served as the ground truth. The network performance was assessed by using fivefold cross-validation. Statistical analysis of the network performance included calculation of lesion detection rates and areas under the receiver operating characteristic curve (AUCs). Results MRI scans from 1008 participants (mean age, 37.7 years ± 9.7; 730 women) were analyzed. At least one enhancing lesion was observed in 519 participants. The sensitivity and specificity averaged across the five test sets were 78% ± 4.3 and 73% ± 2.7, respectively, for slice-wise prediction. The corresponding participant-wise values were 72% ± 9.0 and 70% ± 6.3. The diagnostic performances (AUCs) were 0.82 ± 0.02 and 0.75 ± 0.03 for slice-wise and participant-wise enhancement prediction, respectively. Conclusion Deep learning used with conventional MRI identified enhanced lesions in multiple sclerosis from images from unenhanced multiparametric MRI with moderate to high accuracy. © RSNA, 2019.

White matter changes in patients with mild traumatic brain injury: MRI perspective

This review focuses on white matter (WM) changes in mild traumatic brain injury (mTBI) as assessed by multimodal MRI. All the peer reviewed publications on WM changes in mTBI from January 2011 through September 2016 are included in this review. This review is organized as follows: introduction to mTBI, the basics of multimodal MRI techniques that are potentially useful for probing the WM integrity, summary and critical evaluation of the published literature on the application of multimodal MRI techniques to assess the changes of WM in mTBI, and correlation of MRI measures with behavioral deficits. The MRI–pathology correlation studies based on preclinical models of mTBI are also reviewed. Finally, the author's perspective of future research directions is described.

Cortical Thickness in Mild Traumatic Brain Injury

Magnetic resonance imaging data were acquired at ∼24 h and ∼3 months post-injury on mild traumatic brain injury (mTBI; n = 75) and orthopedic injury (n = 60) cohorts. The mTBI subjects were randomly assigned to a treatment group with atorvastatin or a non-treatment mTBI group. The treatment group was further divided into drug and placebo subgroups. FreeSurfer software package was used to compute cortical thickness based on the three dimensional T1-weighted images at both time-points. Cross-sectional analysis was carried out to compare cortical thickness between the mTBI and control groups. Longitudinal unbiased templates were generated for all subjects and cortical thickness measurements were compared between baseline and follow-up scans in the mTBI group. At baseline, significant reduction in cortical thickness was observed in the left middle temporal and the right superior parietal regions in the mTBI group, relative to the control group (p = 0.01). At follow-up, significant cortical thinning was again observed in the left middle temporal cortex in the mTBI group. Further analysis revealed significant cortical thinning only in the non-treatment group relative to the control group. In the follow-up, small regions with significant but subtle cortical thinning and thickening were seen in the frontal, temporal, and parietal lobes in the left hemisphere in the non-treatment group only. Our results indicate that cortical thickness could serve as a useful measure in identifying subtle changes in mTBI patients.

Effect of cocaine dependence on brain connections: clinical implications

Cocaine dependence (CD) is associated with several cognitive deficits. Accumulating evidence, based on human and animal studies, has led to models for interpreting the neural basis of cognitive functions as interactions between functionally related brain regions. In this review, we focus on magnetic resonance imaging (MRI) studies using brain connectivity techniques as related to CD. The majority of these brain connectivity studies indicated that cocaine use is associated with altered brain connectivity between different structures, including cortical-striatal regions and default mode network. In cocaine users some of the altered brain connectivity measures are associated with behavioral performance, history of drug use, and treatment outcome. The implications of these brain connectivity findings to the treatment of CD and the pros and cons of the major brain connectivity techniques are discussed. Finally potential future directions in cocaine use disorder research using brain connectivity techniques are briefly described.

Effect of in-painting on cortical thickness measurements in multiple sclerosis: A large cohort study

A comprehensive analysis of the effect of lesion in-painting on the estimation of cortical thickness using magnetic resonance imaging was performed on a large cohort of 918 relapsing-remitting multiple sclerosis patients who participated in a phase III multicenter clinical trial. An automatic lesion in-painting algorithm was developed and implemented. Cortical thickness was measured using the FreeSurfer pipeline with and without in-painting. The effect of in-painting was evaluated using FreeSurfer's paired analysis pipeline. Multivariate regression analysis was also performed with field strength and lesion load as additional factors. Overall, the estimated cortical thickness was different with in-painting than without. The effect of in-painting was observed to be region dependent, more significant in the left hemisphere compared to the right, was more prominent at 1.5 T relative to 3 T, and was greater at higher lesion volumes. Our results show that even for data acquired at 1.5 T in patients with high lesion load, the mean cortical thickness difference with and without in-painting is ∼2%. Based on these results, it appears that in-painting has only a small effect on the estimated regional and global cortical thickness. Hum Brain Mapp 36:3749-3760, 2015. © 2015 Wiley Periodicals, Inc.

Multi-modal MRI of mild traumatic brain injury

Multi-modal magnetic resonance imaging (MRI) that included high resolution structural imaging, diffusion tensor imaging (DTI), magnetization transfer ratio (MTR) imaging, and magnetic resonance spectroscopic imaging (MRSI) were performed in mild traumatic brain injury (mTBI) patients with negative computed tomographic scans and in an orthopedic-injured (OI) group without concomitant injury to the brain. The OI group served as a comparison group for mTBI. MRI scans were performed both in the acute phase of injury (~24 h) and at follow-up (~90 days). DTI data was analyzed using tract based spatial statistics (TBSS). Global and regional atrophies were calculated using tensor-based morphometry (TBM). MTR values were calculated using the standard method. MRSI was analyzed using LC Model. At the initial scan, the mean diffusivity (MD) was significantly higher in the mTBI cohort relative to the comparison group in several white matter (WM) regions that included internal capsule, external capsule, superior corona radiata, anterior corona radiata, posterior corona radiata, inferior fronto-occipital fasciculus, inferior longitudinal fasciculus, forceps major and forceps minor of the corpus callosum, superior longitudinal fasciculus, and corticospinal tract in the right hemisphere. TBSS analysis failed to detect significant differences in any DTI measures between the initial and follow-up scans either in the mTBI or OI group. No significant differences were found in MRSI, MTR or morphometry between the mTBI and OI cohorts either at the initial or follow-up scans with or without family wise error (FWE) correction. Our study suggests that a number of WM tracts are affected in mTBI in the acute phase of injury and that these changes disappear by 90 days. This study also suggests that none of the MRI-modalities used in this study, with the exception of DTI, is sensitive in detecting changes in the acute phase of mTBI.

Effect of intrinsic and extrinsic factors on global and regional cortical thickness

Global and regional cortical thicknesses based on T1-weighted magnetic resonance images acquired at 1.5 T and 3 T were measured on a relatively large cohort of 295 subjects using FreeSurfer software. Multivariate regression analysis was performed using Pillai's trace test to determine significant differences in cortical thicknesses measured at these two field strengths. Our results indicate that global cortical thickness is not affected by the field strength or gender. In contrast, the regional cortical thickness was observed to be field dependent. Specifically, the cortical thickness in regions such as parahippocampal, superior temporal, precentral and posterior cingulate is thicker at 3 T than at 1.5 T. In contrast regions such as cuneus and pericalcarine showed higher cortical thickness at 1.5 T than at 3 T. These differences appear to be age-dependent. The differences in regional cortical thickness between field strengths were similar in both genders. Further, male vs. female differences in regional cortical thickness were observed only at 1.5 T and not at 3 T. Our results indicate that magnetic field strength has a significant effect on the estimation of regional, but not global, cortical thickness. In addition, the pulse sequence, scanner type, and spatial resolution do not appear to have significant effect on the measured cortical thickness.

Chronic cocaine administration causes extensive white matter damage in brain: diffusion tensor imaging and immunohistochemistry studies

The effect of chronic cocaine exposure on multiple white matter structures in rodent brain was examined using diffusion tensor imaging (DTI), locomotor behavior, and end point histology. The animals received either cocaine at a dose of 100mg/kg (N=19), or saline (N=17) for 28 days through an implanted osmotic minipump. The animals underwent serial DTI scans, locomotor assessment, and end point histology for determining the expressions of myelin basic protein (MBP), neurofilament-heavy protein (NF-H), proteolipid protein (PLP), Nogo-A, aquaporin-4 (AQP-4), and growth associated protein-43 (GAP-43). Differences in the DTI measures were observed in the splenium (scc) and genu (gcc) of the corpus callosum (cc), fimbria (fi), and the internal capsule (ic). A significant increase in the activity in the fine motor movements and a significant decrease in the number of rearing events were observed in the cocaine-treated animals. Reduced MBP and Nogo-A and increased GAP-43 expressions were most consistently observed in these structures. A decrease in the NF-H expression was observed in fi and ic. The reduced expression of Nogo-A and the increased expression of GAP-43 may suggest destabilization of axonal connectivity and increased neurite growth with aberrant connections. Increased GAP-43 suggests drug-induced plasticity or a possible repair mechanism response. The findings indicated that multiple white matter tracts are affected following chronic cocaine exposure.

Improved three-dimensional Look-Locker acquisition scheme and angle map filtering procedure for T1 estimation

The three-dimensional (3D) Look-Locker (LL) acquisition is a widely used fast and efficient T1 mapping method. However, the multi-shot approach of 3D LL acquisition can introduce reconstruction artifacts that result in intensity distortions. Traditional 3D LL acquisition generally utilizes a centric encoding scheme that is limited to a single phase-encoding direction in k space. To optimize k-space segmentation, an elliptical scheme with two phase-encoding directions is implemented for the LL acquisition. This elliptical segmentation can reduce the intensity errors in the reconstructed images and improve the final T1 estimation. One of the major sources of error in LL-based T1 estimation is a lack of accurate knowledge of the actual flip angle. A multi-parameter curve-fitting procedure can account for some of the variability in the flip angle. However, curve fitting can also introduce errors in the estimated flip angle that can result in incorrect T1 values. A filtering procedure based on goodness of fit (GOF) is proposed to reduce the effect of false flip angle estimates. Filtering based on GOF weighting can remove probable incorrect angles that result in bad curve fitting. Simulation, phantom and in vivo studies have demonstrated that these techniques can improve the accuracy of 3D LL T1 estimation.

Evaluation of fiber tracking from subsampled q-space data in diffusion spectrum imaging

Diffusion spectrum imaging (DSI) is capable of resolving crossing and touching fiber bundles in a given voxel. Acquisition of DSI data involves sampling large number of points in the q-space which significantly increases scan times. The scan times can be reduced by exploiting the symmetry of the q-space. In this study the fiber pathways for five (fornix, cingulum, superior longitudinal fasciculus, corticospinal tract, and crossing fibers in the centrum semiovale region) fiber bundles derived using three subsampled data sets of different sizes derived from the 257 samples in the q-space are compared. The coefficient of variation of the ratio of the number of fiber pathways for each subsample data set to the original data points, averaged over all the 10 subjects, was used for quantitatively investigating the effect of subsampling on the tractography. The effect of threshold angles on tractography is also investigated. The effect of subsampling on the orientation distribution function (ODF) was quantitatively evaluated using both scalar and vector measures derived from the ODF. A streamline tractography method that improves the curvature problem and reduces the local truncation error to further improve the mapping of fiber pathways is adapted. Analysis of the fiber pathways in ten normal subjects, based on qualitative and quantitative methods, shows that the 129 and 198 q-space points provide very similar result with angle of threshold between 41° and 45°. Based on the scan time advantage, 129 subsampled points appear to be adequate for tractography.

Regional cortical thickness in relapsing remitting multiple sclerosis: A multi-center study

A comprehensive analysis of the global and regional values of cortical thickness based on 3D magnetic resonance images was performed on 250 relapsing remitting multiple sclerosis (MS) patients who participated in a multi-center, randomized, phase III clinical trial (the CombiRx Trial) and 125 normal controls. The MS cohort was characterized by relatively low clinical disability and short disease duration. An automatic pipeline was developed for identifying images with poor quality and artifacts. The global and regional cortical thicknesses were determined using FreeSurfer software. Our results indicate significant cortical thinning in multiple regions in the MS patient cohort relative to the controls. Both global cortical thinning and regional cortical thinning were more prominent in the left hemisphere relative to the right hemisphere. Modest correlation was observed between cortical thickness and clinical measures that included the extended disability status scale and disease duration. Modest correlation was also observed between cortical thickness and T1-hypointense and T2-hyperintense lesions. These correlations were very similar at 1.5 T and 3 T field strengths. A much weaker inverse correlation between cortical thickness and age was observed among the MS subjects compared to normal controls. This age-dependent correlation was also stronger in males than in females. The values of cortical thickness were very similar at 1.5 T and 3 T field strengths. However, the age-dependent changes in both global and regional cortical thicknesses were observed to be stronger at 3 T relative to 1.5 T.

Diffusion tensor imaging of forearm nerves in humans

PURPOSE

To implement a diffusion tensor imaging (DTI) protocol for visualization of peripheral nerves in human forearm.

MATERIALS AND METHODS

This Health Insurance Portability and Accountability Act (HIPAA)-compliant study was approved by our Institutional Review Board and written informed consent was obtained from 10 healthy participants. T(1) - and T(2) -weighted turbo spin echo with fat saturation, short tau inversion recovery (STIR), and DTI sequences with 21 diffusion-encoding directions were implemented to acquire images of the forearm nerves with an 8 channel knee coil on a 3T MRI scanner. Identification of the nerves was based on T(1) -weighted, T(2) -weighted, STIR, and DTI-derived fractional anisotropy (FA) images. Maps of the DTI-derived indices, FA, mean diffusivity (MD), longitudinal diffusivity (λ(//) ), and radial diffusivity (λ(⟂) ) along the length of the nerves were generated.

RESULTS

DTI-derived maps delineated the forearm nerves more clearly than images acquired with other sequences. Only ulnar and median nerves were clearly visualized on the DTI-derived FA maps. No significant differences were observed between the left and right forearms in any of the DTI-derived measures. Significant variation in the DTI measures was observed along the length of the nerve. Significant differences in the DTI measures were also observed between the median and ulnar nerves.

CONCLUSION

DTI is superior in visualizing the median and ulnar nerves in the human forearm. The normative data could potentially help distinguish normal from diseased nerves.

Multi-task functional MRI in multiple sclerosis patients without clinical disability

While the majority of individuals with multiple sclerosis (MS) develop significant clinical disability, a subset experiences a disease course with minimal impairment even in the presence of significant apparent tissue damage on magnetic resonance imaging (MRI). Functional magnetic resonance imaging (fMRI) in MS patients with low disability suggests that increased use of the cognitive control system may limit the clinical manifestation of the disease. The current fMRI studies tested the hypothesis that nondisabled MS patients show increased recruitment of cognitive control regions while performing sensory, motor and cognitive tasks. Twenty two patients with relapsing-remitting MS and an Expanded Disability Status Scale (EDSS) score of ≤1.5 and 23 matched healthy controls were recruited. Subjects underwent fMRI while observing flashing checkerboards, performing right or left hand movements, or executing the 2-back working memory task. Compared to control subjects, patients demonstrated increased activation of the right dorsolateral prefrontal cortex and anterior cingulate cortex during the performance of the working memory task. This pattern of functional recruitment also was observed during the performance of non-dominant hand movements. These results support the mounting evidence of increased functional recruitment of cognitive control regions in the working memory system of MS patients with low disability and provide new evidence for the role of increased cognitive control recruitment in the motor system.

Effect of vascular endothelial growth factor treatment in experimental traumatic spinal cord injury: in vivo longitudinal assessment

Vascular endothelial growth factor (VEGF) is thought to provide neuroprotection to the traumatically injured spinal cord. We examined whether supplementing the injured environment with VEGF(165) via direct intraspinal injection into the lesion epicenter during the acute phase of spinal cord injury (SCI) results in improved outcome. The effect of treatment was investigated using longitudinal multi-modal magnetic resonance imaging (MRI), neurobehavioral assays, and end-point immunohistochemistry. We observed on MRI that rats treated with VEGF(165) after SCI had increased tissue sparing compared to vehicle-treated animals at the earlier time points. However, these favorable effects were not maintained into the chronic phase. Histology revealed that VEGF(165) treatment resulted in increased oligodendrogenesis and/or white matter sparing, and therefore may eventually lead to improved functional outcome. The increase in spared tissue as demonstrated by MRI, coupled with the possible remyelination and increased neurosensory sensitivity, suggests that VEGF(165) treatment may play a role in promoting plasticity in the sensory pathways following SCI. However, VEGF-treated animals also demonstrated an increased incidence of persistent allodynia, as indicated on the von Frey filament test.

Fast algorithm for calculation of inhomogeneity gradient in magnetic resonance imaging data

PURPOSE

To develop and implement a new approach for correcting the intensity inhomogeneity in magnetic resonance imaging (MRI) data.

MATERIALS AND METHODS

The algorithm is based on the assumption that intensity inhomogeneity in MR data is multiplicative and smoothly varying. Using a statistically stable method, the algorithm first calculates the partial derivative of the inhomogeneity gradient across the data. The algorithm then solves for the gradient field and fits it to a parametric surface. It was tested on both simulated and real human and animal MRI data.

RESULTS

The algorithm is shown to restore the homogeneity in all images that were tested. On real human brain images the algorithm demonstrated superior or comparable performance relative to some of the commonly used intensity inhomogeneity correction methods such as SPM, BrainSuite, and N3.

CONCLUSION

The proposed algorithm provides an alternative method for correcting the intensity inhomogeneity in MR images. It is shown to be fast and its performance is superior or comparable to algorithms described in the published literature. Due to its generality, this algorithm is applicable to MR images of both humans and animals.

In vivo longitudinal MRI and behavioral studies in experimental spinal cord injury

Comprehensive in vivo longitudinal studies that include multi-modal magnetic resonance imaging (MRI) and a battery of behavioral assays to assess functional outcome were performed at multiple time points up to 56 days post-traumatic spinal cord injury (SCI) in rodents. The MRI studies included high-resolution structural imaging for lesion volumetry, and diffusion tensor imaging (DTI) for probing the white matter integrity. The behavioral assays included open-field locomotion, grid walking, inclined plane, computerized activity box performance, and von Frey filament tests. Additionally, end-point histology was assessed for correlation with both the MRI and behavioral data. The temporal patterns of the lesions were documented on structural MRI. DTI studies showed significant changes in white matter that is proximal to the injury epicenter and persisted to day 56. White matter in regions up to 1 cm away from the injury epicenter that appeared normal on conventional MRI also exhibited changes that were indicative of tissue damage, suggesting that DTI is a more sensitive measure of the evolving injury. Correlations between DTI and histology after SCI could not be firmly established, suggesting that injury causes complex pathological changes in multiple tissue components that affect the DTI measures. Histological evidence confirmed a significant decrease in myelin and oligodendrocyte presence 56 days post-SCI. Multiple assays to evaluate aspects of functional recovery correlated with histology and DTI measures, suggesting that damage to specific white matter tracts can be assessed and tracked longitudinally after SCI.

Effect of cocaine on structural changes in brain: MRI volumetry using tensor-based morphometry

Magnetic resonance imaging (MRI) was performed in cocaine-dependent subjects to determine the structural changes in brain compared to non-drug using controls. Cocaine-dependent subjects and controls were carefully screened to rule out brain pathology of undetermined origin. Magnetic resonance images were analyzed using tensor-based morphometry (TBM) and voxel-based morphometry (VBM) without and with modulation to adjust for volume changes during normalization. For TBM analysis, unbiased atlases were generated using two different inverse consistent and diffeomorphic nonlinear registration techniques. Two different control groups were used for generating unbiased atlases. Independent of the nonlinear registration technique and normal cohorts used for creating the unbiased atlases, our analysis failed to detect any statistically significant effect of cocaine on brain volumes. These results show that cocaine-dependent subjects do not show differences in regional brain volumes compared to non-drug using controls.

Neuronal and axonal degeneration in experimental spinal cord injury: in vivo proton magnetic resonance spectroscopy and histology

Longitudinal in vivo proton magnetic resonance spectroscopy (1H-MRS) and immunohistochemistry were performed to investigate the tissue degeneration in traumatically injured rat spinal cord rostral and caudal to the lesion epicenter. On 1H-MRS significant decreases in N-acetyl aspartate (NAA) and total creatine (Cr) levels in the rostral, epicenter, and caudal segments were observed by 14 days, and levels remained depressed up to 56 days post-injury (PI). In contrast, the total choline (Cho) levels increased significantly in all three segments by 14 days PI, but recovered in the epicenter and caudal, but not the rostral region, at 56 days PI. Immunohistochemistry demonstrated neuronal cell death in the gray matter, and reactive astrocytes and axonal degeneration in the dorsal, lateral, and ventral white-matter columns. These results suggest delayed tissue degeneration in regions both rostrally and caudally from the epicenter in the injured spinal cord tissue. A rostral-caudal asymmetry in tissue recovery was seen both on MRI-observed hyperintense lesion volume and the Cho, but not NAA and Cr, levels at 56 days PI. These studies suggest that dynamic metabolic changes take place in regions away from the epicenter in injured spinal cord.

Symmetric inverse consistent nonlinear registration driven by mutual information

A nonlinear viscoelastic image registration algorithm based on the demons paradigm and incorporating inverse consistent constraint (ICC) is implemented. An inverse consistent and symmetric cost function using mutual information (MI) as a similarity measure is employed. The cost function also includes regularization of transformation and inverse consistent error (ICE). The uncertainties in balancing various terms in the cost function are avoided by alternatively minimizing the similarity measure, the regularization of the transformation, and the ICE terms. The diffeomorphism of registration for preventing folding and/or tearing in the deformation is achieved by the composition scheme. The quality of image registration is first demonstrated by constructing brain atlas from 20 adult brains (age range 30-60). It is shown that with this registration technique: (1) the Jacobian determinant is positive for all voxels and (2) the average ICE is around 0.004 voxels with a maximum value below 0.1 voxels. Further, the deformation-based segmentation on Internet Brain Segmentation Repository, a publicly available dataset, has yielded high Dice similarity index (DSI) of 94.7% for the cerebellum and 74.7% for the hippocampus, attesting to the quality of our registration method.

Blood-spinal cord barrier permeability in experimental spinal cord injury: dynamic contrast-enhanced MRI

After a primary traumatic injury, spinal cord tissue undergoes a series of pathobiological changes, including compromised blood-spinal cord barrier (BSCB) integrity. These vascular changes occur over both time and space. In an experimental model of spinal cord injury (SCI), longitudinal dynamic contrast-enhanced MRI (DCE-MRI) studies were performed up to 56 days after SCI to quantify spatial and temporal changes in the BSCB permeability in tissue that did not show any visible enhancement on the post-contrast MRI (non-enhancing tissue). DCE-MRI data were analyzed using a two-compartment pharmacokinetic model. These studies demonstrate gradual restoration of BSCB with post-SCI time. However, on the basis of DCE-MRI, and confirmed by immunohistochemistry, the BSCB remained compromised even at 56 days after SCI. In addition, open-field locomotion was evaluated using the 21-point Basso-Beattie-Bresnahan scale. A significant correlation between decreased BSCB permeability and improved locomotor recovery was observed.

Diffusion tensor imaging of cocaine-treated rodents

Studies in cocaine-dependent human subjects have shown differences in white matter on diffusion tensor imaging (DTI) compared with non-drug-using controls. It is not known whether the differences in fractional anisotropy (FA) seen on DTI in white matter regions of cocaine-dependent humans result from a pre-existing predilection for drug use or purely from cocaine abuse. To study the effect of cocaine on brain white matter, DTI was performed on 24 rats after continuous infusion of cocaine or saline for 4 weeks, followed by brain histology. Voxel-based morphometry analysis showed an 18% FA decrease in the splenium of the corpus callosum (CC) in cocaine-treated animals relative to saline controls. On histology, significant increase in neurofilament expression (125%) and decrease in myelin basic protein (40%) were observed in the same region in cocaine-treated animals. This study supports the hypothesis that chronic cocaine use alters white matter integrity in human CC. Unlike humans, where the FA in the genu differed between cocaine users and non-users, the splenium was affected in rats. These differences between rodent and human findings could be due to several factors that include differences in the brain structure and function between species and/or the dose, timing, and duration of cocaine administration.

Magnetic resonance spectroscopy in the monitoring of multiple sclerosis

In addition to providing information on tissue structure, magnetic resonance (MR) technology offers the potential to investigate tissue metabolism and function. MR spectroscopy (MRS) offers a wealth of data on the biochemistry of a selected brain tissue volume, which represent potential surrogate markers for the pathology underlying multiple sclerosis (MS). In particular, the N-acetylaspartate peak in an MR spectrum is a putative marker of neuronal and axonal integrity, and the choline peak appears to reflect cell-membrane metabolism. On this basis, a diminished N-acetylaspartate peak is interpreted to represent neuronal/axonal dysfunction or loss, and an elevated choline peak represents heightened cell-membrane turnover, as seen in demyelination, remyelination, inflammation, or gliosis. Therefore, MRS may provide a unique tool to evaluate the severity of MS, establish a prognosis, follow disease evolution, understand its pathogenesis, and evaluate the efficacy of therapeutic interventions, which complements the information obtained from the various forms of assessment made by conventional MR imaging.